CHAPTER IV 

 THE CELL 



In the simplest forms of animal life the entire body consists of a 

 little albuminous structure, the essential pecuUarity of which is that 

 it possesses properties which we recognize as characteristic of living 

 organisms. This albuminous material basis of Hfe is known as pro- 

 toplasm, while the structure itself is known as a cell. All plants and 

 animals consist of cells and their derivatives, and if an attempt be 

 made to resolve any of the more complex living structures into its 



Fig. I. — Diagram of a typical cell, i, Cell membrane. 2, Metaplasm granules. 

 3, Karyosome or net-knob. 4, Hyaloplasm. 5, Spongioplasm. 6, Linin network. 

 7. Xucleoplasm. 8, Attraction-sphere. 9, Centrosome. 10, Plastids. 11, Chro- 

 matin network. 12, Nuclear membrane. 13, Nucleolus. 14, Vacuole. 



component elements, it is found that the smallest possible subdivi- 

 sion still compatible with life is the cell. The cell may therefore be 

 considered as the histological element or unit of structure. While 

 presenting fundamental similarities which define them, cells vary 

 greatly in size, shape and structure. Thus in the human body the 

 cells vary in size from the small lymphocyte with a diameter of about 

 4M to the giant cells of bone marrow with a diameter up to loo^t. 

 Cells also vary greatly in shape from the typical spherical of the 

 ovum to the very irregular stellate multipolar cells of the nervous 



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